CD-ROM Magazin 1995 June/CDROM6.BIN/share100/wwplus/formats.tx_/formats.tx

Text File | 1995-02-17 | 5KB | 121 lines

FORMATS.TXT

File to accompany WWPlus
Copyright ⌐1994-1995 by
Don Bradner
Arcata Pet
600 F Street
Arcata, CA 95521

WWPlus allows many standard graphics formats to be used
as Windows wallpaper, including .BMP, the only format directly
recognized by Windows.

The formats involve a tradeoff of disk space versus time.
The most compressed formats take the longest to decompress.
For the user, the decision must be made based on available
space and the inconvenience of having the system pause
during wallpaper changes.

Users of disk compression software such as Stacker will usually
find that there is little advantage in using a compressed
format (other than JPEG), since the disk utility will do as
good a job as any of the compressed formats.  Best choice in
that case is almost always .BMP.

A discussion of each format follows:

.BMP and .RLE
This is the fastest format available, but requires the most
disk space.  It does not require any conversion or
decompression by WWPlus, so the only time required to
display a new wallpaper is the time it takes to read the image
from the disk.  Excellent for small images that are "tiled"
(displayed as multiple images to cover the desktop space).
This format is usable for all color levels from 16 to
16-million.  .RLE is a compressed form of .BMP.

.ICO
These are Windows icon files, 32x32 pixels and 16 colors.  You
may use these as tiled wallpaper with WWPlus.  The temporary
.BMP file that WWPlus creates will have a color depth equal to
the maximum number of colors that your monitor will support.

.TIF and .TGA
These formats offer minimal if any disk space savings over
.BMP, while requiring time for WWPlus to convert them to
.BMP format for use by Windows.  The only reason to leave an
image in these formats is to maintain compatibility with some
other program.  Otherwise they would be best converted to .BMP or
one of the compressed formats.  .TIF is usable for all color
levels, 16 to 16-million, while .TGA is usable from 256 to
16-million.

.PCX
This format, which can be read and written by Windows
Paintbrush but not used directly as wallpaper, offers some
compression for images with color levels up to 256.
Decompression and conversion by WWPlus is fairly fast.
The .PCX format can use color levels up to 16 million, but file
size actually increases when 24-bit files are used.

.GIF The Compuserve Graphics Interchange Format offers great
compression of images up to 256 colors without loss of
quality.  It is not usable for images with more colors.  This
format is generally the best choice when disk space is limited
and the image has no more than 256 colors.  There is a
noticable delay while WWPlus decompresses the image and
converts it to .BMP for display, although the faster the
computer the shorter the delay.  The .GIF format contains
compression technology that is patented by the Unisys
corporation, and as of 1/1/95 became liable for royalty
payments by software developers.  See the full statement in the
README.TXT file.

.JPG
JPEG (Joint Photographic Experts Group - the
committee which formulated the standard), is designed to
compress 24-bit (16-million color) images.  Unlike .GIF and
.PCX compression, JPEG causes some loss of quality in the
image, so it is called "lossy."

JPEG does a very good job of compression, and with most
pictures the resulting image is comparable to the original.
There is a variable amount of compression available, with
greater loss of quality as the image is further compressed.
WWPlus allows a quality setting of 5 to 95, with 5 being the
most compressed and 95 being the least compressed.  A 622,134
byte test file produced sizes of 5,381 bytes at a setting of 5,
and 75,809 bytes at a setting of 95.  The image was very
deteriorated at the lower setting, while it was indistinguishable
from the original at 95.  Further testing for this image showed
very acceptable results at a setting of 75, with a file size of
25,554 bytes.

JPEG does not work very well with images of 256 colors or less,
and is particularly unsuited for images with large areas of
solid colors and sharp edges.

The delay in decompressing a JPEG file is considerable.  It
will vary depending on the speed of the computer, but is slow
even on a fast machine.  Users of the JPEG option may want to
turn off the timed wallpaper changes and use the manual change
options within WWPlus when the decompression time is not going
to hinder other work.  With Windows NT or Windows 95 it may be
possible to completely perform decompression in the background;
at this time it is not possible with regular Windows and WWPlus.

Editing a JPEG image and saving it in .JPG format again will
result in additional losses of quality.  Editing should always
be performed on the original 24-bit image before compression is
done.

There are many non-standard forms of JPEG.  WWPlus should
read any JPEG image conforming to the JFIF standard, but may
not be able to read images produced by non-standard programs.
An example would be GIF2JPG, which can produce a proprietary
JPEG file called HSI.  Older versions of the program did this
by default; newer versions produce JFIF compatible files by
default.